Northern Pikeminnow Predation on Juvenile Chinook Salmon and Potential Impacts to Local Populations
Richard A. Carmichael1,✉, Nicholas J. Porter1, Kevin E. See1,2, Michael S. Hall1, Tara E. Blackman3, and Michael W. Ackerman1,3
12 November, 2021
Abstract
Abstract text here.
1 Biomark, Inc., 705 South 8th Street, Boise, Idaho, 83702, USA
2 Washington Department of Fish and Wildife, Under A Bridge, Seattle, Washington, 00000, USA
3 Mount Hood Environmental, PO Box 4282, McCall, Idaho, 83638, USA
✉ Correspondence: Richard A. Carmichael <Richard.Carmichael@merck.com>
Keywords: northern pikeminnow; Chinook salmon; predation; mark-recapture; bioenergetics
Introduction
The Upper Salmon River major population group (MPG) supports eight independent, extant spring/summer Chinook Salmon Oncorhynchus tshawytscha populations including Salmon River (above Redfish Lake), Valley Creek, Yankee Fork Salmon River, East Fork Salmon River, Salmon River (mainstem below Redfish), Pahsimeroi River, Lemhi River, and North Fork Salmon River (NOAA 2017). At least five of these eight populations must meet criteria set forth by McElhany et al. (2000) and ICTRT (2007) for the MPG to be considered viable and for the recovery of the Snake River Evolutionary Significant Unit (ESU). Populations within the ESU have substantial cultural value, support downriver mainstem Snake and Columbia River commercial and subsistence fisheries, and support local fisheries and economies in years with sufficient abundance. All populations within the Upper Salmon River MPG have become depleted in recent decades. Declines in survival of juvenile Chinook Salmon have been attributed to the removal of beavers from the landscape (fur trade), mining activities, river simplification, water withdrawals, logging activities, urbanization, avian predation, proliferation of non-native species (e.g., non-native coastal rainbow trout O. mykiss irideus and brook trout Salvelinus fontinalis), warming streams and rivers, and modifications to downriver migration corridors (e.g., from hydropower projects). Moreover, the abundance of returning adults are further impacted by ocean and downriver harvests, poor ocean conditions, and changes to the spawning migration corridor. Each of these factors have contributed, to varying and unknown extents, to reduced adult escapement, the primary metric used to assess population viability. In response to the decline in Chinook Salmon abundance from the myriad human activities and associated habitat degradation, action agencies have attempted to improve juvenile survival and adult spawning conditions by investing in the rehabilitation of tributary ecosystems.
Paragraph 2
One potentially important, but perhaps under-appreciated source of mortality on Chinook salmon is predation on emigrating juveniles by piscivorous fishes, including both native and non-native species. As an example,…
- At this point, I’m thinking leave avian predation out of the equation, but instead include in Discussion
- and keep focus on the freshwater environment
- What is known about downriver (Columbia/Snake) piscivorous fish populations and potential predation on juvenile Chinook salmon?
- literature review of northern pikeminnow, smallmouth bass, other? predation on juvenile Chinook salmon, particulary from the Snake and Columbia rivers
- still stay away from avian predation
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- Summary of findings from Axel et al. (2015) and early RT reports and papers (Ackerman et al. (2018), Porter et al. (2019), Porter et al. (2020)) in Deadwater Slough. Recent studies have demonstrated decreased movement and survival of juvenile salmonids emigrating through the Deadwater Slough. Axel et al. (2015) demonstrated decreased rates of emigration and survival for sockeye salmon Oncorhynchus nerka from Redfish Lake emigrating during the spring and recent winter telemetry studies have indicated decreased transition probabilities (approximately 10% less than nearby reaches) of juvenile Chinook salmon Oncorhynchus tschawytscha through Deadwater Slough during fall and winter months (Ackerman et al. (2018), Porter et al. (2019), Porter et al. (2020)).
- Axel et al. (2015) found increased mortality in a particular reach spanning location x to location y in the mainstem Salmon River on a study of juvenile (hatchery?) sockeye salmon released near Redfish Lake and actively migrating downriver.
- in their case, these were actively migrating juveniles, and so transitional probabilities can likely be interpreted (almost) directly as survival
- A previous study showed that the lowest transitional probabilities of Red Fish Lake Sockeye occurred in the Dead Water reach.
- Ackerman et al. (2018) and Porter et al. (2019), Porter et al. (2020) found reduced (apparent) survival in a reach spanning near the town of North Fork to just downstream of Deadwater Slough.
- in these cases, there’s a chance that juvenile Chinook could exhibit concealment behavior prior to winter and so transition probability is interpreted as the probability of a fish surviving AND moving
- Anecdotally, locals (and others? maybe NOAA?) informed us that northern pikeminnow and perhaps other species are prevalent in Deadwater Slough.
Spring/summer Chinook Salmon in the Upper Salmon MPG are stream-type and exhibit two distinct migration tactics; downstream rearing (DSR) and natal reach rearing (NRR) (Copeland et al. 2014). The DSR migrants leave the natal spawning area as subyearlings between June and November and typically overwinter in downstream, mainstem habitats until the following spring when they emigrate to the ocean as smolts. Alternatively, NRR migrants remain in their natal spawning areas for approximately one year after emergence until emigration to the ocean as smolts. Diversity of migratory tactics provides a mechanism for coping with adverse conditions in freshwater rearing and migration environments and buffers against catastrophic events, thereby increasing population resiliency.
The Deadwater Slough is located in a reach of the Salmon River that is believed to be a historically important overwinter rearing area for DSR emigrants. Moreover, this reach is part of the migratory pathway for juvenile DSR and NRR emigrants from all eight extant populations. The slough lacks hydrological and structural features (i.e., a homogenous channel with fine substrate and little cover) that can provide essential refuge from predation. As a result, predation on juvenile Chinook salmon proximal to the Deadwater Slough has been cited as a concern for the Upper Salmon River MPG, impacting DSR migrants in the fall and NRR emigrants during the spring.
We hypothesize that increased densities of piscivorous predators in the Deadwater Slough area may explain the reduced survival (or apparent survival) observed for juvenile Chinook Salmon (Ackerman et al. 2018) and Sockeye Salmon (Axel et al. 2015). In this study, we estimated the abundance of a piscivorous fish predator population in the Deadwater Slough and their potential impacts to juvenile salmon emigrants, focusing on DSR and NRR Chinook Salmon. Our objectives for the study were four-fold:
- Estimate the abundance (or relative abundance) of potential predators in the Deadwater Slough during the peaks of fall (DSR) and spring (NRR) juvenile emigrations.
- Document predation on juvenile Chinook Salmon during the emigration periods using gastric lavage.
- Use a bioenergetics approach to estimate the total consumption of juvenile DSR and NRR Chinook salmon during defined emigration periods.
- Quantify the potential impacts of estimated predation on juvenile to Chinook Salmon adult returns.
We follow with a discussion of the various assumptions that went into the mark-recapture and bioenergetics models and assessment of impacts to adult returns and how violations of some assumptions may affect overall results and inferences from the study.
Methods
Study Site
The Deadwater Slough is an approximately 1.5 kilometer section of the mainstem Salmon River located roughly 5.8 river kilometers downstream from the town of North Fork, Idaho (Figure 3). The downstream end of the slough is located at the confluence of Dump Creek and the Salmon River. Around 1897, the failure of a small mining diversion reservoir in the Dump Creek drainage resulted in an erosion event that deposited substantial amounts of sediment at the confluence of the Salmon River, thereby creating an unnaturally slow and deep section in the river, spanning approximately 30 acres and averaging 68 m width. Both northern pikeminnow Ptychocheilus oregonensis and smallmouth bass Micropterus dolomieu inhabit the slough which likely provides favorable conditions for their feeding and growth (e.g., reduced water velocity, deep channel, warmer water temperature).
Abundance of Piscivorous Fishes (Objective 1)
Data = C/M/R and Effort
- Capture methods used - We initially attempted electrofishing, snorkeling, netting, others?, but eventually settled on angling as best method for mark-recapture.
- Mark-recapture - We kept the mark and recapture events close together in an attempt to use a closed population model
- What are the assumptions of a closed population model?
- How was sampling performed? What relevant information was captured for each fish? How/where were fish released? How was effort recorded to calculate CPUE?
- Description of sampling time frame:
- Fall 2019: Goal was to estimate abundance during the peak of DSR emigration i.e., timing was done to coincide to be shortly after peak fall (DSR) emigration at the lower Lemhi River screw trap with the hopes of documenting predation. DSR are the more abundant juvenile emigration tactic.
- Fall 2020: Intent was to repeat the above, but instead during peak NRR emigration, but effort canceled due to COVID-19. Instead, sampling was re-schedule to fall when social distancing, etc. could be put in place.
- Spring 2021: Did a relative abundance effort during spring 2021. Had to reduce to a CPUE (single-week) effort due to funding constraints. However, goal was to 1) document presence during NRR outmigration and 2) estimate CPUE to provide a relative comparison to the fall efforts.
The Lincoln-Petersen estimator is below, where \(M\) is the number of fish marked and returned to the population, \(n\) is the number of fish caught in the second/recapture event and \(m\) is the number of marked fish in the second sample.
\[ \hat{N} = \frac{(M)(n)}{(m)} \]
The Lincoln-Petersen estimator can be biased with small samples, so we also investigated the Chapman-modified Lincoln-Petersen estimator which is shown below. \[ \hat{N} = \frac{(M + 1)(n + 1)}{(m + 1)} - 1 \] The Schnabel estimator is shown below, where the \(M\), \(n\) and \(m\) are indexed by the sampling occasion, \(i\). In our example, the sampling occasions are defined as each day of sampling. This estimator does not have an associate standard error, but 95% confidence intervals can be calculated. \[ \hat{N} = \frac{\sum\limits_{i = 1}^k n_i M_i}{\left(\sum\limits_{i = 1}^k m_i \right) + 1} \] There is another estimator for this type of multiple census surveys, called the Schumacher-Eschmeyer estimator, which is based on minimizing the weighted sum of squares between the proportion of marked individuals in the sample and the unknown proportion of marked individuals in the population. It is shown below.
\[ \hat{N} = \frac{\sum\limits_{i = 1}^k n_i M^2_i}{\sum\limits_{i = 1}^k m_i M_i} \]
Predation Upon Juvenile Chinook Salmon i.e., Gastric Lavage (Objective 2)
Data = Gastric Lavage Data
The goal was to document predation upon juvenile Chinook salmon (or other targets), and ideally, estimate the proportion of their diet that consisted of juvenile Chinook salmon at the time of sampling?
- Which individuals was gastric lavage performed upon?
- How was gastric lavage performed?
- Intent was to quantify predation on juvenile Chinook salmon
- or incidentally, juvenile steelhead or sockeye salmon
We collected stomach contents from most captured individuals using gastric lavage (Foster (1977)) and examined contents for the presence or absence of juvenile Chinook salmon and other incidentals (e.g., steelhead, sockeye salmon) juveniles and the proportion of stomach contents containing targets versus non-targets (e.g., macroinvertebrates). Stomach contents were stored in whirl-paks, preserved with 99% isopropyl alcohol, and analyzed one week later in a controlled environment. Each sample was uniquely identified to match up with the appropriate fish record, contents were identified down to its unique composition, total weight of all content was measured in grams, and total weight of fish content, if found, was measured in grams. Throughout the sampling period a proportion of the captured individuals were sacrificed after gastric lavage to validate that the gastric lavage was successful at flushing all or most of the stomach contents from the northern pikeminnow.
Bioenergetics (Objective 3)
Data = Temperature, Bioenergetics Inputs, Others?
Pull material from technical report
Impacts to Adult Returns (Objective 4)
Data = SARs, Adult Escapements, Others?
Pull material from technical report
- After making some assumptions (e.g., on SARs) attempt to estimate how results from objective #3 could translate into impacts on adult returns (via a thought experiment or simulation approach)
Results
Abundance of Piscivorous Fishes (Objective 1)
| Sampling Event | Estimator | N | SE | Lci | Uci |
|---|---|---|---|---|---|
| Fall 2019 | Chapman | 13,298 | 4,322.3 | 6,898 | 27,893 |
| Fall 2019 | Petersen | 15,105 | 5,658.3 | 7,331 | 37,569 |
| Fall 2019 | Schnabel | 18,732 |
|
10,057 | 37,851 |
| Fall 2019 | Schumacher-Eschmeyer | 20,615 |
|
14,393 | 36,313 |
| Fall 2020 | Chapman | 24,882 | 9,253.8 | 11,784 | 56,907 |
| Fall 2020 | Petersen | 29,700 | 13,170.0 | 12,727 | 91,470 |
| Fall 2020 | Schnabel | 37,556 |
|
18,698 | 82,105 |
| Fall 2020 | Schumacher-Eschmeyer | 43,279 |
|
23,061 | 351,090 |
Figure 1: Estimates of abundance of northern pikeminnow using different estimators.
Figure 2: Total catch per unit effort across entire sampling event.
- Total population estimates of Pike Minnow. Chart or table, but likely a chart.
- What is that equate to as a density? e.g., how many pikeminnow per 10 square meters? Is that a reasonable number?
Predation Upon Juvenile Chinook Salmon i.e., Gastric Lavage (Objective 2)
- Gastric lavage sampling results. What percent of the diet is chinook salmon from each sampling event. Pie chart? Mike loves pie charts.
Bioenergetics (Objective 3)
- Water Temperature measurements.
- Hobo tidbit placed at site.
- Calculated daily average water temperature for 365 days of the year.
- Water temperature plot for the 365 average.
- Bioenergetics results. Total mass consumed over a 365 day period. Plot of daily consumption with day of year on x and mass on y.
Impacts to Adult Returns (Objective 4)
- SAR results. Maybe a plot of multiple scenarios depending on gastric lavage results? And pop estimates if they vary in time.
Discussion
We estimated the population size of Northern Pikeminnow in the Deadwater Slough to be greater than xx,xxx during the fall emigration period for DSR Chinook Salmon. That estimate translates to a density of xxx Northern Pikeminnow per 100 m or xxx per 100 m2 which is similar/more/less than estimates from elsewhere in the Columbia River (citation) where substantial Northern Pikeminnow predation impacts on salmonids have led to bounty programs aimed at reducing Northern Pikeminno abundance. The population size of Northern Pikeminnow was not directly estimated during the spring NRR Chinook salmon emigration period however, the relative abundance measured at CPUE was comparable to the fall sampling periods (update statement later). The population of Northern Pikeminnow in Deadwater Slough was estimated to consume between xx,xxx and xx,xxx juvenile Chinook Salmon during the x sampling periods and result in an estimated reduction of returning adults between xxx and x,xxx. We suggest that the habitat modifications that created the Deadwater Slough reach have resulted in favorable conditions for Northern Pikeminnow, including improved conditions for predation upon juvenile Chinook Salmon (add detail here). Therefore, predation by Northern Pikeminnow in the Deadwater Slough likely has a consequential impact on ESA-listed Chinook Salmon populations in the Upper Salmon River MPG.
Mark-Recapture Model
Re-hash out our assumptions? What assumptions were most likely violated e.g., the closed population assumption? If we assumed an open population with varying immigration/emigration rates how might that affect our estimate? In the end, how good do we think our estimate is and is the bottom-line that we belive there still to be a shit-ton of pikeminnow even if our assumptions were violated?
Gastric Lavage
Concerns with gastric lavage. We only observed juvenile Chinook salmon (and/or other fishes) in a very small number of stomach contents. However, we don’t necessarily believe that to mean that pikeminnow in Deadwater Slough rarely consume juvenile Chinook salmon. Are there other cases where gastric lavage failed to document predation? How soon after consumption do you need to take a sample? So instead, we made some assumptions about the proportion of a pikeminnows diet consisting of Chinook salmon.
Bioenergetics
What assumptions did we make during the bioenergetics assessment? And how might violations of those assumptions change our estimate of the number of juvenile Chinook salmon consumed and resulting impacts to adult returns?
Impacts to Adult Returns
Again, what assumptions did we make here and how might violations of those assumptions change our estimate of impacts to adult returns.
Avian Predation
Although not formally assessed in this study, avian predators including Great Blue Herons Ardea herodias and Bald Eagles Haliaeetus leucocephalus are another potential source of mortality for juvenile salmon in the Deadwater Slough. The Deadwater Slough is recognized as an important bird watching and nesting area due to the riparian and backwater habitats created by the feature (Deadwater Slough - Audubon Important Bird Areas). Several piscivorous bird species have been documented using the Deadwater Slough that include the Common Mergus merganser and Hooded Lophodytes cucullatus mergansers, the Great Blue Heron, the Double-crested Cormorant Phalacrocorax auritus, and the Belted Kingfisher Megaceryle alcyon (eBird 2021). During the intial sampling event in 2019, a two-person crew walked the entire reach and surrounding and upstream areas scanning for passive integrated transponder (PIT) tags. During that informal survey, nine PIT tags were recovered near active bird nests or in an upstream anastomizing reach where herons and eagles are prevalent, suggesting that mortality may have been a result of avian predation. The PIT tag histories in PTAGIS indicate these tags were implanted into a combination of juvenile Chinook Salmon (3), Sockeye Salmon (3), and steelhead (3). Avian predation contributes a major component of the total mortality for yearling Chinook Salmon in some locations in the lower Snake River and Columbia River, particularly at hydroelectric dams and within reservoirs (Evans et al. 2012; 2016); however, we did not observe large colonies of piscivorous birds within the study area. Although there is documentation of individual Double-crested Cormorants (eBird 2021) at the Deadwater Slough, the site is not within their breeding range, rather, it is part of a migration corridor. Given the current avian species known to occupy Deadwater Slough, it is unlikely that avian predation on juvenile salmonids is comparable to elsewhere in the Columbia River basin with large piscivorous bird colonies. Nevertheless, we hypothesize that the reservoir-like conditions at the Deadwater Slough may increase the probability of avian predation on juvenile Chinook Salmon from the many piscivorous birds known to use the site. Future estimates of predation would benefit from consideration of the contribution of piscivorous avian predators.
Management Implications
Discuss the potential for various management actions: * Removing the Dump Creek alluvial fan and restoring flow. What would that look like? * A local bounty program? What would that look like? Have they been successful elsewhere e.g., in the Columbia River?
Deadwater is an opportunity to benefit multiple (6 or 7) local populations with a single management or restoration action.
Also, this is an anthropogenically created dead water area, which could be a candidate for restoration (removing the impoundment). Is there anything in the literature that discusses habitat preferences for pike minnow? If we speed up velocities and add some cover potentially pike minnow predation success will be lowered. Will these fish just move elsewhere?
Conclusions
- We have also presented a novel modeling framework for estimating predation on native, critically endangered anadromous species which can be applied to other areas of interest. John day? Others?
- The end.
Acknowledgements
Literature Cited
Tables
Figures
